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=Chorismate synthase=

Chorismate Synthase is the last enzyme present in the shikimate pathway, a process which converts phosphoenolpyruvate, and erythrose 4-phosphate to chorismate in a series of seven steps. The shikimate pathway is essential in the production of the amino acids phenylalanine, tryptophan and tyrosine, all essential amino acids.

=Structure= This protein is in a unique form containing four subunits, and forming a homotetramer. The protein also contains a unique β-α-β sandwich fold.  The protein also has a cofactor bound within each monomer of the protein. This cofactor is FMN which is located within the active site of the protein. Each of these cofactors are bound non-covalently within the protein in the reduced form.

Function
The purpose of chorismate synthase is to convert 5-enolpyruvylshikimate 3-phosphate to chorismate, an essential step in the formation of indole rings used in the essential amino acids phenylalanine, tyrosine, and tryptophan. The reduced flavin is believed to have one of a couple functions. It either has a structural role helping with formation of the structure, or reduces a sulfhydryl group in the protein residue, either aiding with binding or with having a catalytic effect. The enzyme is monofunctional, requiring another enzyme to reduce the flavin cofactor, or addition of extra reduced flavin to add to the enzyme. =Mechanism= In this reaction the 5-enolpyruvylshikimate 3-phosphate, is reduced forming a second double bond in the benzene ring attached to the phosphate. It appears that the phosphate group is reduced allowing the benzene ring to have a free electron pair to form a double bond with. As well the double bond which originally existed, experiences a hydrogen shift and the second double bond occurs to form resonance. =References=